This invention relates to polyvinyl butyral (PVB) sheet used with glass in safety laminates.
PVB sheet is widely used in association with one or more layers of glass in a laminate for architectural windows, automobile windshields, skylights and the like. The interlayer sheet may chemically degrade, discolor or fade when the glass laminate in use is exposed to ultraviolet (UV) rays from sunlight over an extended period. UV absorber is usually in the sheet formulation to prevent or minimize this.
Moisture on the order of up to about 2 weight percent of the sheet can be absorbed from a hot, humid environment during preparation of the glass laminate or later in use around the exposed sheet edge. This is undesirable since it causes delamination from the glass around the border of the laminate.
Adhesion control agent (ACA) in the sheet formulation controls adhesion of the sheet to glass to provide energy absorption on impact of the glass laminate. Though suitable for this, some ACA's result in zero adhesion at high interlayer moisture levels. Multivalentmetal salts of organic monocarboxylic acids control such adhesion and are desirably relatively insensitive to sheet moisture absorption. Unfortunately, the present inventors found that multivalent metal salts in PVB sheet adversely affect its UV stability even in the presence of certain UV absorbers.